Electric motors use electrical energy to produce mechanical energy, very typically through the interaction of magnetic fields and current-carrying conductors. The conversion of electrical energy into mechanical energy by electromagnetic means was first demonstrated by the British scientist Michael Faraday in 1821 and later quantified by the work of Hendrik Lorentz.
A magnetic field is generated when electric charge carriers such as electrons move through space or within an electrical conductor. The geometric shapes of the magnetic flux lines produced by moving charge carriers (electric current) are similar to the shapes of the flux lines in an electrostatic field. Magnetic flux passes through most metals with little or no effect, with certain exceptions, notably iron and nickel. These two metals, and alloys and mixtures containing them, are known as ferromagnetic materials because they concentrate magnetic lines of flux. Areas of greatest field strength or flux concentration are known as magnetic poles.
In a traditional electric motor, a central core of tightly wrapped current carrying material creates magnetic poles (known as the rotor) which spins or rotates at high speed between the fixed poles of a magnet (known as the stator) when an electric current is applied. The central core is typically coupled to a shaft which will also rotate with the rotor. The shaft may be used to drive gears and wheels in a rotary machine and/or convert rotational motion into motion in a straight line.
Generators are usually based on the principle of electromagnetic induction, which was discovered by Michael Faraday in 1831. Faraday discovered that when an electrical conducting material (such as copper) is moved through a magnetic field (or vice versa), an electric current will begin to flow through that material. This electromagnetic effect induces voltage or electric current into the moving conductors.
Current power generation devices such as rotary alternator/generators and linear alternators rely on Faraday's discovery to produce power. In fact, rotary generators are essentially very large quantities of wire spinning around the inside of very large magnets. In this situation, the coils of wire are called the armature because they are moving with respect to the stationary magnets (which are called the stators). Typically, the moving component is called the armature and the stationary components are called the stator or stators.
Motors and generators used today produce or utilize a sinusoidal time varying voltage. This waveform is inherent to the operation of these devices.
In most conventional motors, both linear and rotating, enough power of the proper polarity must be pulsed at the right time to supply an opposing (or attracting) force at each pole segment to produce a particular torque. In conventional motors at any given instant only a portion of the coil pole pieces is actively supplying torque.
With conventional motors a pulsed electrical current of sufficient magnitude must be applied to produce a given torque/horsepower. Horsepower output and efficiency then is a function of design, electrical input power plus losses.
With conventional generators, an electrical current is produced when the rotor is rotated. The power generated is a function of flux strength, conductor size, number of pole pieces and speed in RPM. However output is a sinusoidal output with the same losses as shown in conventional electric motors.
A conventional linear motor/generator, on the other hand, may be visualized as a typical electric motor/generator that has been cut open and unwrapped. The “stator” is laid out in the form of a track of flat coils made from aluminum or copper and is known as the “primary” of a linear motor. The “rotor” takes the form of a moving platform known as the “secondary.” When the current is switched on, the secondary glides past the primary supported and propelled by a magnetic field. A Linear generator works in the same manner but mechanical power provides the force to move the rotor or secondary past magnetic fields.
In traditional generators and motors, the pulsed time varying magnetic fields produces undesired effects and losses, i.e. Iron Hystersis losses, Counter-EMF, inductive kickback, eddy currents, inrush currents, torque ripple, heat losses, cogging, brush losses, high wear in brushed designs, commutation losses and magnetic buffeting of permanent magnets. In many instances, complex controllers are used in place of mechanical commutation to address some of these effects.
In motors and generators that utilize permanent magnets it is desirable to increase magnetic flux densities to achieve more efficient operation. Most permanent magnet motor/generators used today rely on permanent magnets such as Neodymium magnets. These magnets are the strongest of the man made magnetic materials. Due to their strategic value to industry and high costs it is desirable to increase flux densities without relying on a breakthrough in material composition of these magnets or manufacturing high density special purpose magnet shapes and sizes.
In motors or generators, some form of energy drives the rotation and/or movement of the rotor. As energy becomes more scarce and expensive, what is needed are more efficient motors and generators to reduce energy costs.